This invention relates generally to metering devices for dispensing or injecting a quantity of lubricant, and in particular to a cap and seal assembly for protecting a metering device from moisture and dirt contamination.
Lubricant metering devices are used to deliver a quantity of oil or grease under pressure to lubrication points on machine tools, vehicles, and heavy equipment. One type of metering device has an injector with a generally cylindric body containing a spring-loaded, reciprocal piston. The device dispenses an accurate amount of lubricant when the piston reciprocally moves in response to pressure variations in a lubricant supply line. These injectors typically have an adjusting screw for controlling the quantity of lubricant dispensed and an indicator pin connected to the piston for providing visual indication of injector operation. The adjusting screw and indicator pin are both located on a narrowed end structure of the injector that projects from an end of the body.
Lubricant metering devices are susceptible to failure when moving parts become contaminated with moisture or dirt. Injectors are frequently grouped in manifold assemblies that are remotely mounted on the machine tools, positioned near the lubrication points that they serve. These injectors encounter difficult environments, including wide temperature variations, exposure to dust particles, and partial immersion in mud or water. Dirt contamination in the end structure inhibits operation of the adjusting screw and indicator pin. Moisture contamination causes corrosion that eventually ruins the injector.
To protect the end structure from dirt and moisture, some injectors incorporate a detachable cap that is placed over the end structure and encloses the adjusting screw and indicator pin. A lower rim of the cap circumferentially engages the injector body. Unfortunately, the rim of the cap does not provide a fluid-tight sealing contact against the injector body. Moisture may freely reach the end structure even when the cap is in place, leaving injectors susceptible to corrosion. It has not previously been found practical to seal the cap because when the cap is placed over the end structure, any seal tends to trap air within the cap and causes a build-up of air pressure which inhibits motion of the cap to its proper position.
Another drawback is that the cap is prone to fall off the injector, especially when the injector is moved to an inverted orientation. To avoid this, some caps have been modified to tightly grip the injector body with a press fit at the cap's rim. However, injector bodies exhibit small non-uniformities in size due to manufacturing tolerances, and each modified cap typically fits only one injector and at one angular position. Thus modified caps lack interchangeability with other caps, substantially degrading their usefulness.